- [Instructor] Previously in this weekly series,I demonstrated how to save render timeby disabling global illumination diffuse raysin the Arnold renderer.Instead I used an Arnold sky dometo provide an even, ambient light.That movie was titledApproximating Global Illumination in Arnold.This week I'll build on that techniqueby adding an ambient occlusion light filter.Here's the image rendered without the light filterand here it is with the light filter applied.

So I'll switch bath and forth between those two imagesa few times so you can see the difference.This is actually the original use case for ambient occlusionway back in the 90s.A flat even wash of illumination is added to the sceneand the distance between surfaces determines how muchof that ambient light is blocked or occluded.The result is darker shading in the corners of rooms,the crevices in and between objectsand anywhere the ambient light would be blocked.

The rendering is not as realistic as global illumination,but it's much faster.If you're rendering high resolution images or animation,you may not want to wait for many hoursto render a single frame.Now here's an image that was renderedwith two diffuse rays or two bounces.It looks good but is fairly grainy.I had to decrease the diffuse sampling up to sixto get this level of quality,which resulted in a render time of over 40 minutes.

Now again, take a look at the same scenerendered with no diffuse rays and the scene wideambient occlusion effect.Again, this doesn't look as realistic,but it rendered in five minutes instead of 40.I was able to use the default value for diffuse sampleswhich is only two, so the trade off is clear.Disabling diffuse bounces and using ambient occlusionmakes the image less realistic, but it rendersan order of magnitude more quickly.This technique relies on an ambient occlusionlight filter for Arnold which is notpart of the standard MAXtoA installation.

Mike Farnsworth at Solid Angle kindly developedthis light filter for Arnold 5 and Mads Drischlercomplied it for MAXtoA,so thank you Mike and thank you Mads.We need to install the light filterin the program file directory,so let's go to Windows Explorer.In the exercise files I provided for this weekly series,I've created a custom folder called plugins.Inside there is a descriptive folder,ambient occlusion light filter for Arnold 5.

Go inside there and there is a plugin DLL file,AO light filter dot DLL.Select it, right click, and copy it.Now go into your program files.It'll be on your system drive, program files,Autodesk, 3ds Max version number, plugins.Inside plugins you'll find MAXtoA.Go in there and paste the file in here.

Right click and paste.You may need to click trough a promptor even provide a password.Now we've saved into the program files directory.We also need to create a Windows environment variable.One way to get there is to right click on the computer iconin my case labeled this PC and then go to its properties.Click on advanced system settingsand then click environment variables.

We need to create a new environment variable.Click the new button and type it injust exactly as you see it here in all capitals,Arnold underscore plugin underscore path.The variable value will be the pathto the file we just copied.We can go back to the Windows Explorer windowand if that path is displayed,we can just right click at the end of itand choose copy address as text and go back to ourenvironment variables, paste that into the variable value,click there, and then right click, choose paste.

Now the path is pasted in.We can click okay, click okayto exit the environment variables.Click okay to exit system propertiesand now with the file in the right placeand the environment variable created for the current user,we can now launch 3ds Max.In this scene, I've got all lights turned offso that we can most clearly see the effectof the ambient occlusion light filter.Let's create an Arnold sky dome.To create it most cleanly,we'll turn on 3D snaps, go to the create panel,lights, from the pull down list, choose Arnold,click the Arnold light button,and in the front view port,click and drag from top to bottomto create the light and its target.

Release the mouse, right click to exit creation mode,go to the modify panel and change the typeover to sky dome.Let's take a look at this in an active shade rendering.I've got that set up already.Click active shade on the main toolbarand it's overexposed.We can go into the light parameters.Under color intensity, reduce the exposuredown to its minimum of negative five.

Now we have light coming through the windows.We actually don't want this.We want an overall wash, so let's turn off cast shadows.Scroll down a little bit more.In shadow, disable cast shadows.Now we have an even flat wash over the entire shot.This is exactly the conditionwe want for a true ambient light.We can fine tune this a little bitby changing its color temperature.Scroll back up a little bit.In color intensity, change the color over tothe type of texture and we need to supply a map.

Click the no map button.In the material map browser, go into the maps OSL sectionand you'll see black body.Select that and click okay.Now we need to adjust the parameters,so let's open up the material editorand drag that map over into the materiel editor view,choose instance, double click it, and rename the node.

We'll call it sky dome color.We just need to change the minimum and maximum values herefor the color temperature.Let's set them both to a value of 4,800 degrees Kelvin.That's giving us a little warmer colorbecause the camera is currently set to 5,000.Now we're ready to add the Arnold light filter.With the light still selected,go back to the modify panel.From the modifier list, choose Arnold light filter.

We need to assign a map.We see that it actually appears in the list hereunder maps, Arnold, AO light filter.So one way we could create this would beto simply open that up and drag it intothe material editor view and then click on its output,hold down the mouse, drag it over to the modify paneland drop it on the no map buttonand then in the instance copy map dialogue,choose instance, click okay.Then double click on that nodeand rename it ambient occlusion.

Let's see what this looks like.Here is our active shade rendering still runningand all we need to do to enable or disable itis turn this modifier on or off.So with it turned off, we have the flat illuminationand then turn it back on again,we can see the ambient occlusion blockingsome of the light.Let's change the far clip value to a value of 10and now we can see that we're only seeingthe occlusion effect where surfacesare close to one another.

Okay, that looks pretty good.We can turn on our ceiling lights.Close the material editor, select one of those lights,and turn it on in its light propertiesand our active shade updatesand we can see the effectof global illumination being faked.Now we can render an animation in 1/10 of the timeand have less grain,although we would be sacrificing some realism.That's how to use an ambient occlusion Arnold light filterto fake diffuse global illumination in Arnold 5.

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Updated

6/3/2020

Released

7/10/2019

3ds Max is a powerful, deep, and multifaceted program, so there's always more to learn. This weekly series aims to keep you on top of the latest tools and techniques, and introduces fresh perspectives on traditional methods for architectural and product visualization, animation, visual effects, games and virtual worlds, and motion graphics. Instructor Aaron F. Ross presents a new topic every week, spanning the full range of 3D graphics tasks, including modeling, rigging and animation, shading and lighting, camera operation, and rendering. He gives special attention to streamlining workflows, such as automation of time-consuming tasks, so your productions run more smoothly and efficiently. Come back every Wednesday for a new tutorial to expand your 3ds Max knowledge and skills.Note: Because this is an ongoing series, viewers will not receive a certificate of completion.